1. Field of the Invention
The invention relates to electrical switchboard apparatus and more particularly to means for connecting the main horizontal bus to the vertical riser bus forming a part of such switchboard apparatus.
2. Description of the Prior Art
An electrical distribution switchboard distributes the main incoming power among various site functions such as heating, lighting, and air conditioning. It typically consists of a number of vertical cabinet sections containing circuit breakers for switching and protecting the various load circuits. Three-phase electrical power enters a switchboard via cable or bus duct connected to a main bus which runs horizontally within the switchboard between the various sections. The main bus is connected to vertical, or riser, bus in each vertical cabinet section. Various circuit interrupters stacked vertically in the cabinet sections have their inputs connected to the vertical riser bus and their outputs connected to horizontal load side extensions which run toward the rear of the cabinet perpendicular to the main horizontal bus. Bus duct or cable is then attached to the load side extensions to permit the power to exit the switchboard and flow to the load (air conditioning, lighting motors, etc.).
The primary requirements for a switchboard are that it be safe and dependable, and that it exhibit low cost in construction, installation, and maintenance. In addition, the switchboard should be of compact construction to reduce space requirements at the user location. The design of the switchboard should include sufficient versatility to allow circuit breakers of various interruption capacities and frame sizes to be easily included in the switchboard.
Specifically, it would be desirable to provide an electrical switchboard with the capacity to stack six 800 amp breakers in a single vertical section while providing the capability to include other frame sizes in a single section, such as four 1600 amp breakers, two 3000 amp breakers, or combinations of different frame size breakers within the same vertical section. Prior art electrical switchboards often required three different positions for the main horizontal bus, depending upon the breaker frame size mix. This required additional engineering design effort to specify the location of the horizontal bus for each individual application, as well as the need for more complex installation procedures. It would be desirable to provide a switchboard having a single location for the main horizontal bus for all breaker frame size mixes.
In producing a cost effective switchboard design, some objections are often in conflict. For example, it is possible to produce a design utilizing a minimum of material but this often dictates the necessity for a large number of different parts to accommodate the wide variety of individual switchboard applications. It would therefore be desirable to provide an electrical switchboard requiring a minimum amount of material and a minimum number of component styles, yet which is easily adaptable to accommodate a large variety of individual applications.
In order to provide such flexibility, it is desirable to have individual component parts perform more than one function. For example, several small lengths of vertical riser bus could be combined to form a variety of total riser bus lengths. By feeding the vertical riser bus at the geometric center, it would be possible to use a single part for both the upper and lower riser bus section.
In addition, it would be desirable to provide a uniform cross-section of vertical riser bus throughout its length. One method of achieving would be to feed the vertical bus in its electrical center. For example, if six 800 amp breakers are stacked in a single vertical section, the total amount of current which can be carried by these circuit breakers is 6 .times. 800 = 4,800 amperes. However, if the associated vertical riser bus is connected to the horizontal main bus at a point midway between the top and bottom circuit breakers, e.g. the electrical center of the vertical riser bus, the amount of current which is required to be carried by any one portion of the vertical riser bus is only one half of the total capacity of the section, since half the current will flow upward into the three upper circuit breakers and half will flow downward into the three lower circuit breakers. Therefore, the total current carrying requirement of any portion of the vertical riser bus is only 3 .times. 800 = 2,400 amperes. It would therefore be desirable to provide an electrical switchboard having the vertical riser bus connected to the main horizontal bus so as to feed the vertical riser bus at its geometric and electrical center.